The fibrosis in the liver which can occur pari passu with chronic hepatocellular injury may arise as a result of increased collagen synthesis by fibroblasts and smooth muscle cells which have migrated to the liver in response to the release of chemotactic factors. The nature of these putative chemotactic factors, their cell of origin and the sequence of events which leads to their release and biological activity are unknown. Using an in vitro assay to measure the response of collagen synthesizing cells to chemotactic factors evidence for the production of these factors is being sought in an animal model of hepatic fibrosis and in patients with chronic hepatocellular disease.